Solid-state imaging devices using charge-coupled devices (CCDs) are known as examples of solid-state imaging devices.
A CCD solid-state image sensor includes multiple photosensor units using photoelectric transducers, that is, photodiodes (PDs) configured to generate and store signal charge of an amount corresponding to the amount of received light, which are arranged in a two-dimensional matrix. The signal charge is generated and stored on the basis of light signals from a subject incident on the photodiodes of the multiple photosensor units. The stored signal charge is transferred in the vertical direction by a vertical transfer register arranged for each column of the photosensor units and transferred in the horizontal direction by a horizontal transfer register having a CCD structure. The signal charge transferred in the horizontal direction is output as image information of the subject from an output unit having a charge-voltage converter.
A solid-state image sensor has multiple pixels composed of multiple photosensor units that are photodiodes arranged in horizontal and vertical directions, reading units, and vertical transfer channels, for example.
Each photosensor unit includes a signal charge storage part and a hole accumulation region formed in a p-type semiconductor well region of a substrate made of an n-type semiconductor.
The signal charge storage part is formed by an n-type impurity region. The hole accumulation region is formed by a p-type impurity region (p+) and formed on the surface of the signal charge storage part.
Each vertical transfer channel is formed in the n-type impurity region at a predetermined distance from the photosensor units. In addition, a p-type impurity region (p) is formed between a vertical transfer channel and a photosensor unit to be read on one side thereof and functions as a reading unit. Furthermore, a horizontal element isolation unit made of a p-type impurity region (p+) is formed between the vertical transfer channel and a photosensor unit that is not to be read on the other side thereof. Furthermore, vertical element isolation units made of p-type impurity regions (p+) are formed at both ends of a photosensor unit.
The horizontal element isolation units isolate the respective photosensor units in the horizontal direction, and the vertical element isolation units isolate the respective photosensor units in the vertical direction. The vertical element isolation units, the horizontal element isolation units, and the reading units are each formed in contact with the vertical transfer channels.
First transfer electrodes and second transfer electrodes are formed alternately above the reading units and the vertical transfer channels with an insulating film therebetween. The vertical transfer channels, the first transfer electrodes, and the second transfer electrodes constitute the vertical transfer registers.
As a method for forming vertical transfer registers in a microcell, a technology of allowing the line widths of vertical transfer channels to be reduced and suppressing occurrence of potential barriers in potential distribution of the vertical transfer channels to improve the efficiency of transferring signal charge has been proposed (refer to Patent Document 1, for example).